Thiocyanogen
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| Names | |
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| Preferred IUPAC name
Cyanic dithioperoxyanhydride | |
| Other names
Dicyanodisulfane
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CompTox Dashboard (EPA)
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| Properties | |
| C2N2S2 | |
| Molar mass | 116.16 g mol−1 |
| Appearance | Colorless crystal or liquid[1]: 241, 255–256 |
| Melting point | −2.5 °C (27.5 °F; 270.6 K)[1]: 241 |
| Boiling point | ≈20 °C (decomposes)[2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Thiocyanogen, (SCN)2, is a
diiodine.[2] This hexatomic compound exhibits C2 point group symmetry and has the connectivity NCS-SCN.[3]
In the
suspension in diethyl ether and excess iodine, but misidentified the minor product as sulfur iodide cyanide (ISCN).[6] Indeed, that reaction suffers from competing equilibria attributed to the weak oxidizing power of iodine; the major product is sulfur dicyanide.[7] The following year, Schneider produced thiocyangen from silver thiocyanate and disulfur dichloride, but the product disproportionated to sulfur and trisulfur dicyanides.[6]
The subject then lay fallow until the
Modern syntheses typically differ little from Söderbäck's process. Thiocyanogen synthesis begins when aqueous solutions of
glacial acetic acid with bromine then affords a 0.1M solution of thiocyanogen that is stable for days.[8] Alternatively, a solution of bromine in methylene chloride is added to a suspension of Pb(SCN)2 in methylene chloride at 0 °C.[9]
- Pb(SCN)2 + Br2 → (SCN)2 + PbBr2
In either case, the oxidation is
exothermic.[1]
: 255
An alternative technique is the
cupric thiocyanate at 35–80 °C:[1]
: 253
- 2Cu(SCN)2 → CuSCN + (SCN)2
In general, thiocyanogen is stored in solution, as the pure compound explodes above 20 °C[2] to a red-orange polymer.[1]: 241 However, the sulfur atoms disproportionate in water:[1]: 241–242 [10]
- 3(SCN)2 + 4H2O → H2SO4 + HCN + 5SCN− + 5H+
Thiocyanogen is a weak
poor metals.[1]: 241 It adds trans to alkenes to give 1,2-bis(thiocyanato) compounds; the intermediate thiiranium ion can be trapped with many nucleophiles.[2] Radical polymerization is the most likely side-reaction, and yields improve when cold and dark.[2][1]: 247 However, the addition reaction is slow, and light may be necessary to accelerate the process.[1]: 247 Titanacyclopentadienes give (Z,Z)-1,4-bis(thiocyanato)-1,3-butadienes, which in turn can be converted to 1,2-dithiins.[9] Thiocyanogen only adds once to alkynes; the resulting dithiocyanatoacyloin is not particularly olefinic.[1]: 247 Selenocyanogen, (SeCN)2, prepared from reaction of silver selenocyanate with iodine in tetrahydrofuran at 0 °C,[11] reacts in a similar manner to thiocyanogen.[9]
Thiocyanogen has been used to estimate the
: 247References
- ^ a b c d e f g h i j k l m Wood, John L. (August 1947) [1946]. "Substitution and addition reactions of thiocyanogen". In Adams, Roger (ed.). Organic Reactions (PDF). Vol. 3 (3rd reprint ed.). New York / London: Wiley / Chapman Hall. pp. 241–266.
- ^ ISBN 978-0-471-93623-7, retrieved 2024-03-30
- .
- .
- ISSN 0893-228X.
- ^ a b c d e Kaufmann, H. P. (1925). "Das freie Rhodan und seine Anwendung in der Maßanalyse. Eine neue Kennzahl der Fette" [Unbound rhodanium and its application to elemental analysis: A new measurement technique for fats]. Archiv der Pharmazie und Berichte der Deutschen Pharmazeutischen Gesellschaft (in German). 263: 675–721 – via HathiTrust.
- ^ .
- ISBN 978-0-470-13232-6.
- ^ .
- ISSN 0022-4944.
- .
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